Fertilisation and Early Embryo Development Flashcards
What is the stimulant for ovulation?
A spike of plasma LH
What are the two types of ovulation?
Spontaneous & induced ovulation
What are the four key evens of ovulation?
Follicular wall bursts, oocyte & granulosa cells released from GC anchor point, oocyte carried with follicular fluid into the peritoneal cavity, captured by fimbria of the infundibulum
What is the difference between the fertilisation period and the fertile period?
Fertilisation period is the time when oocytes are available to be fertilised by sperm, fertile period is the time when mating could result in pregnancy
When does ovulation occur in canine species?
Ovulation occurs at metaphase of meiosis I, completion of meiosis II and formation of second polar body occurs after fertilisation – this means, unlike other species, the fertilisation period is not immediately after ovulation (actually 2 days to 5 days after)
What three events must sperm go through in order for fertilisation to occur?
Sperm capacitation, sperm binding, acrosome reaction
What are the two binding sites for sperm?
Primary zona binding region & acrosome reaction promoting ligand
What is the function of the sperm and egg membrane fusion?
Allows sperm nuclei passage into egg cytoplasm
What two events are stimulated by sperm membrane fusion?
Causes depolarisation of egg membrane & the cortical reaction (cortical granules are released into the perivitelline space – changes ZP3 so that sperm can no longer bind)
What happens during the second meiotic division?
Oocyte activation & extrusion of second polar body
What is an ootid?
When the two pronuclei are both visible in the cell
What do the two pronuclei fuse to form?
A zygote
What are cleavage divisions?
A series of mitotic divisions undergone by the zygote
What are the cells of the two-cell embryo called?
Blastomeres
What is the 16 cell embryo formed from subsequent divisions of the blastomere called?
Morula
When does totipotency cease?
Beyond the 16-cell stage
What do the outer and inner cells within the morula form?
Outer cells form cell-cell adhesions called tight junctions -> trophoblast – chorion and placenta
Inner cells have looser lines of communication called gap junctions -> inner cell mass – embryonic disc
How does a blastocyst form?
Outer cells pump sodium into the morula, ionic concentration therefore rises and water then diffuses through the zona pellucida – fluid accumulation
How does hatching of the blastocyst occur?
Proteolytic enzymes are produced by trophoblast, zona pellucida weakens, zona pellucida splits and the blastocyst emerges (hatching)
What is uterine milk/histiotroph?
Secretions derived from the endometrial glands containing carbohydrate, proteins and lipids that provide nutritional support to the blastocyst before the placenta is established
What are the three types of embryo progression?
Slow, continuous progression – rabbit, sow
Discontinuous progression – cow, ewe, human – prolonged stay in the uterine tube
Fertilised progression – mare – only fertilised eggs pass into uterus
Which three layers make up the primary germ layers?
Outer ectoderm and inner endoderm, later a third layer (mesoderm) is produced
What does the ICM give rise to?
Epiblast – forms anionic ectoderm & Hypoblast – form primitive endoderm (yolk sac)
What happens to the extraembryonic mesoderm?
Continues to grow and forms a sac that surrounds the yolk, and folds dorsally to form the amniotic folds
How does the allantois form?
From an out-pouching of the hindgut
What is the chorion?
Membranes between the developing fetus and the mother – formed by extraembryonic mesoderm and the two layers of trophoblast
Where does gastrulation begin?
At the posterior end of the embryo
What happens during gastrulation?
Cells from the epiblast migrate through the primitive streak and differentiate into ectoderm, mesoderm and endoderm
